In a computer system, working voltage of a Central Processing Unit (CPU) is configured to vary with its working mode, and a voltage regulator is configured to provide an output voltage to power the CPU. In order to meet the demand for the output voltage at different working modes of the CPU, the voltage regulator is configured to receive a voltage identification code sent by the CPU and is configured to modulate the output voltage according to the voltage identification code.
FIG. 1 illustrates a circuit block diagram 100 of a traditional power system for the CPU. The CPU 21 is configured to send a voltage identification code VID to the voltage regulator 20, the voltage regulator 20 is configured to provide an output voltage Vo for a capacitor C1 according to the voltage identification code VID, and the output voltage Vo is the working voltage of the CPU 21. However, a variation period of the voltage identification code VID is uncontrollable, so a variation period of a current Icap flowing through the capacitor C1 may enter into an audible range, so the power system may produce audible noises.